Increasing freezing point of food with sea buckthorn ice nucleating agent

ABSTRACT

The freezing point of a food product subjected to freezing temperatures is increased by adding to the food product a juice obtained from berries of sea buckthorn or an aqueous extract obtained from sea buckthorn berry or leaf tissue. The food product containing the added sea buckthorn substance is then cooled to freeze the product.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.08/344,210, filed Nov. 23, 1994.

BACKGROUND OF THE INVENTION

The subject of the present invention is an ice nucleating agent and aprocess for preparing such an agent.

It is known that a product can be frozen in the presence of an icenucleating agent, at a temperature greater than that where this productwould have frozen spontaneously. Indeed, ice nucleating agents promoteformation of ice crystals at a temperature greater than that where thesecrystals would have formed without the presence of nucleating agents.Thus, such agents are up until now used in processes for freezingproducts, especially food products, in order to reduce the quantity ofenergy necessary for the freezing of these products European PatentApplication Publication No. 0 424 771 A1.

It is also known that ice nucleating agents can increase the size of icecrystals during the freezing of some products (Ryder, J. M. 1987,Thesis, p155, Rhode Island University). Indeed, the ice crystals presentin a product frozen with an ice nucleating agent are larger than thosepresent in the same product frozen without such an agent. These largeice crystals leave, moreover, an imprint in the European PatentApplication Publication No. 0 424 771 A1 frozen products by modifyingtheir texture. Furthermore, this modification can be stablilized byfreeze-drying followed by heating of the frozen product. Thus, icenucleating agents are up until now used for freezing products,especially food products, in order to give an advantageous texture tothe final product (Agric. Biol. Chem., 50 (1), 169-175, 1986).

Most biological nucleating agents have been found in microorganisms orinsects. However, it could be very useful to isolate an ice nucleatingagent from plants, especially from edible plants, for their use for thefreezing, texturing or cryoconcentration of products, such as foodproducts for example.

The aim of the present invention is to respond to this need.

SUMMARY OF THE INVENTION

The ice nucleating agent according to the present invention is an icenucleating agent obtained from sea buckthorn (Hippophae). It may be anaggregate comprising a protein part and a lipid part. Moreover, seabuckthorn may be in particular Hippophae rhamnoides, Hippophaesalicifolia, Hippophae tibetana or Hippophae neurocarpa. It has beenfound that the raw juice of the sea buckthorn berries contains the icenucleating agent and that the agent may be obtained and contained in anaqueous extract by aqueously extracting tissue of the berries and of theleaves.

All plants which are part of the genus Hippophae are sea buckthorns.Moreover, this shrub is widely distributed in Europe and in Asia, andhas the advantage of producing numerous orange berries. Sea buckthorn isthus an abundant source of ice nucleating agent.

In addition to obtaining the ice nucleating agent by recovering rawjuice from the berries, the present invention includes a process forobtaining the agent, wherein berry and/or leaf tissue is extracted withan aqueous solution containing a saccharide to obtain an aqueous extractpart and a solids part and then the aqueous extract part is separatedfrom the solids part to obtain the aqueous extract part containing theagent.

DETAILED DESCRIPTION OF THE INVENTION

In this description, the term "agent" or "nucleating agent" is used inthe sense of "ice nucleating agent".

In carrying out the invention, preferably, ripe sea buckthorn berries(that is to say berries which have ripened until they have an orangecolour), and in particular sea buckthorn berries having a water contentof 80% to 90%, are used for example. The berries can thus be ground orcrushed by pressing or by centrifugation, and then the resulting rawjuice can be recovered for use as an ice nucleating agent, for example.

As the tissues of the berry and in particular its outer coat contain alarge quantity of nucleating agent, it is also possible to extractdirectly the berries with an extraction solution comprising pectin,mono-, oligo- and/or polysaccharides, and preferably with at least oneof these solutions comprising, in water, 0.0001 to 2% by weight ofpectins of all degrees of esterification, for example, or 0.0001 to 2%by weight of at least one of the other saccharides.

In particular, the extraction solution is chosen from the groupconsisting of solutions of alginates, polygalacturonic acid, amylose,amylopectin, polymannans, arabinose, galactose, lactose, glucose,fructose and sucrose.

In order to carry out this extraction, it is thus possible to crush orgrind the berries, for example, to add to the volume of berries thusobtained 1 to 200 volumes of at least one of the said extractionsolutions, but preferably 5 to 100 volumes, and then to allow the wholeto react for 1 to 30 min at a temperature of 4 to 35° C., and finally toseparate a solid part by centrifugation or by filtration of the mixture,for example, and to harvest a liquid part having a nucleating activity.

Preferably, the berries of the solid part of the extracted mixture aresubjected to at least 1 new extraction as described above. For that, theberries of the solid part of the extraction mixture can be resuspendedeach time in one of the said extraction solutions, a solid part can thenbe separated and a liquid extract harvested. It has thus been possibleto observe that the nucleating activity of the various successiveextracts remains identical during at least the first 25 extractions. Itis however preferable to first remove the raw juice from the berriesbefore extracting therefrom the nucleating agent several times insuccession. Indeed, this crude juice contains sugars, flavourings andproteins which are damaging to the nucleating activity.

Likewise, in order to obtain an extract from sea buckthorn leaves,leaves can be finely ground and then the nucleating agent extractedtherefrom in the same manner as described above by at least one of thesaid saccharide composition solutions of pectin, mono-, oligo- and/orpolysaccharide, for example.

Because the sea buckthorn berries are edible and traditionally used inthe manufacture of liqueurs and jams, a crude extract of sea buckthornberry can thus be used directly as natural additive for the preparationof food products, for the purpose of freezing them, texturing them orcryoconcentrating them, for example.

In a process for freezing a product, it is thus possible to add the saidice nucleating agent to a freezable product and to freeze the saidproduct between -5° C. and -25° C. The advantage of using the agentaccording to the invention lies in the fact that it is possible to carryout the freezing at high temperatures between -5° C. and -10° C. forexample, and that the additive is perfectly edible.

In another process for texturing food products, the said ice nucleatingagent is added to a freezable product, the said product is frozenbetween -5° C. and -25° C., the said product is freeze-dried and thenheated. The advantage of using the agent according to the invention liesin the fact that it is possible to carry out the freezing at hightemperatures between -5° C. and -10° C., for example, that the additiveis perfectly edible and that the crystals are large in size, bringingabout, as a result, improved modification of the texture of the product.

Finally, it is also possible to cryoconcentrate a liquid, such as acoffee extract, a fruit juice or a vegetable juice, by adding thereto anextract comprising the agent according to the present invention, byfreezing it between -5° C. and -10° C., and then by separating thecrystalline phase from the liquid phase by centrifugation, for example.The advantage of using the agent according to the invention lies in thefact that it is possible to carry out the freezing at high temperaturebetween -5° C. and -10° C. for example, that the additive is perfectlyedible, that the crystals are large in size, bringing about, as aresult, improved separation of the phases, and that the crystallizationrate is relatively high thus accelerating as a result the wholecryoconcentration process.

BRIEF DESCRIPTION OF THE DRAWING FIGURE

The Drawing Figure illustrates ice nucleating activity of raw juice withreference to berry maturity.

TEST METHODS, EXAMPLES AND FURTHER DESCRIPTION WITH REFERENCE TO THEDRAWING FIGURE

The ice nucleating agent according to the present invention is describedin greater detail by means of the various properties determinedespecially using various tests, as set out below. The percentages aregiven by weight, unless otherwise stated.

Measurement of the nucleating activity of sea buckthorn extracts obtainof juice and extracts of sea buckthorn berries:

Sea buckthorn (Hippophae rhamnoides) berries are harvested at maturityand then stored frozen at -40 ° C. until used. The juices and extractsare preserved at 4° C.

Extract 1 (crude berry juice): the berries are thawed, crushed and thencentrifuged in an Eppendorf tube (5000 g_(n), 10 min) at 20° C. Thesupernatant is used.

Extract 2 (ground berries): the frozen berries are intensely ground in aPOLYTRON grinder for 5 min. The juice containing the berry skins isused.

Extract 3 (ground berry supernatant): the ground berries are centrifuged(5000 g_(n), 10 min) at 4° C. The supernatant is used.

Extract 4 (ground berry pellet): after centrifugation of previouslyground berries, the pellet is taken up in 3 volumes of water which areused.

Extracts 5 to 7: a pellet of ground and centrifuged berries is taken upin 25 volumes of a solution comprising 0.01, 0.1 or 0,5% pectin inwater, the whole is allowed to react for 15 min while stirringoccasionally, the mixture is centrifuged (10,000 g_(n), 10 min), thenthe supernatant is used as extract.

Extracts 8 to 9: a pellet of ground and centrifuged berries is extractedin the same manner as for extracts 5 to 7 with 2 volumes of a solutioncomprising 0.001 or 0.0001% pectin in water.

Extracts 10 to 22: a pellet of ground and centrifuged berries isextracted in the same manner as for extracts 5 to 7, with respectivelysolutions comprising 0.1% pectin at various degrees of esterification(10%, 38%, 75%), or with solutions comprising respectively 0.1%polygalacturonic acid, 0.1% amylose, 0.1% amylopectin, 0.01% alginate,1% polymannans (polysaccharide fraction of coffee), 0.1% galactose, 0.1%glucose, 0.01% arabinose and 0.01% sucrose.

Nucleating activity:

The nucleating activity of an agent present in a product is measured bymeasuring the temperature at which the product freezes. This temperatureis called nucleating temperature. This temperature is then compared tothat obtained with the product containing no agent (control). Anucleating activity is observed when the nucleating temperature of theproduct containing the agent is greater than that of the controlproduct.

The nucleating activity can be characterized according to threetemperatures: the ice nucleating temperatures (in °C.) T20, T50, T80indicating that respectively 20%, 50% and 80% of the samples freeze atthis temperature.

In the description which follows, the term "nucleating point" will beused in the sense of "nucleating temperature at which 50% of the samplesare frozen", that is to say the T50 value.

Drop test: the above-mentioned samples 1 to 4 (10°) are diluted 10 to1000 fold (10⁻¹ to 10⁻³) with double distilled water or a strawberryjuice. Ten drops of 10 μl of extract are deposited on an aluminium foilcoated with paraffin, and the foil is placed on a water bath cooled at arate of 0.1° C. per minute. All the dilutions are on the same foil. TheT20, T50 and T80 values are then determined.

The strawberry juice is prepared by centrifugation of fresh, previouslywashed strawberries (kitchen centrifuge) followed by a secondcentrifugation of the juice at 4° C. (10,000 g_(n), 15 min). Thesupernatant is then stored frozen at -20° C., and then thawed beforebeing used as model.

Glass tube test: 100 ml of the above-mentioned extracts 5 to 22, diluted10 fold in double distilled water, are added to a thin-walled glass tubewhich is then placed in a water bath cooled at a rate of 0.1° C./min.The T20, T50 and T80 values are then determined.

Table 1 below presents for the above-mentioned samples 1 to 4 theresults of the trials carried out according to the drop test.

As can be seen, a marked difference is observed between the nucleatingtemperatures of the samples (dilution up to 10⁻²) and that of the samplefrozen without agent (control). In contrast, the nucleating activity ofa raw berry juice diluted 1/1000 is relatively low. Furthermore, avariation is generally observed between the nucleating temperatures ofthe crude samples (10°) and those of the diluted samples. The highconcentration of sugar in the crude samples would probably disrupt thenucleating activity of the agent.

                  TABLE 1                                                         ______________________________________                                                Double distilled water                                                                      Strawberry juice                                        Sample                                                                              Dilution                                                                              T20     T50   T80   T20  T50   T80                              ______________________________________                                        1     10.sup.0                                                                              -7.3    -7.4  -7.9  -6.7 -7.0  -7.1                                   10.sup.-1                                                                             -6.8    -7.1  -7.9  -6.4 -6.8  -7.2                                   10.sup.-2                                                                             -6.8    -8.9  < -9  -7.2 -7.4  -8.3                                   10.sup.-3                                                                             < -9.0  < -9.0                                                                              < -9.0                                                                              -7.5 -8.5  -9.0                             2     10.sup.0                                                                              -7.3    -7.7  -7.9  -6.7 -6.9  -7.0                                   10.sup.-1                                                                             -5.9    -6.6  -6.9  -6.6 -6.8  -6.9                                   10.sup.-2                                                                             -6.2    -7.7  < -9.0                                                                              -7.2 -7.5  -7.7                                   10.sup.-3                                                                             -6.8    < -9.0                                                                              < -9.0                                                                              -7.1 -7.7  -8.4                             3     10.sup.0                                                                              -7.3    -7.3  -7.7  -7.0 -7.3  -7.4                                   10.sup.-1                                                                             -6.4    -6.7  -7.3  -7.2 -7.4  -7.5                                   10.sup.-2                                                                             -7.2    -7.6  -7.8  -7.4 -7.6  -7.8                                   10.sup.-3                                                                             -8.0    -8.9  < -9.0                                                                              -7.8 -7.9  -8.7                             4     10.sup.0                                                                              -5.9    -6.5  -6.6  -5.7 -6.0  -6.2                                   10.sup.-1                                                                             -5.9    -6.5  -6.9  -6.6 -6.7  -7.4                                   10.sup.-2                                                                             -6.4    -6.8  -8.7  -7.5 -7.9  -8.2                                   10.sup.-3                                                                             -7.4    -8.8  < -9.0                                                                              -8.4 < -9.0                                                                              < -9.0                           Control                                                                             10.sup.0                                                                              < -10   < -10 < -10 -9.4 < -10 < -10                            ______________________________________                                    

Table 2 below presents for extracts 5 to 22 the results of the trialscarried out according to the glass tube test.

                  TABLE 2                                                         ______________________________________                                        Extract No.             T20    T50    T80                                     ______________________________________                                         5. 0.5% pectin             -5.0   -5.0 -5.5                                   6. 0.1% pectin             -5.0   -5.0 -5.5                                   7. 0.01% pectin            -5.0   -5.0 -5.5                                   8. 0.001% pectin           -5.5   -5.5 -5.5                                   9. 0.0001% pectin          -5.5   -5.5 -5.5                                  Controls                                                                      Extract No. 5 filtered using a 0.45 μm membrane                                                    -5.5   -5.5   -5.5                                    0.5% pectin solution    -9.5   -11.5  -12                                     Filtered 0.5% pectin solution (0.45 μm)                                                            -9.0   -11.5  -12                                     10. 0.1% pectin (10% of esters)                                                                           -5.5   -5.5 -6.0                                  11. 0.1% pectin (38% of esters)                                                                           -5.0   -5.0 -5.5                                  12. 0.1% pectin (75% of esters)                                                                           -5.5   -5.5 -5.5                                  13. 0.1% polygalacturonic acid                                                                            -5.0   -5.5 -5.5                                  14. 0.1% amylose            -5.5   -6.0 -6.5                                  15. 0.1% amylopectin        -5.5   -6.0 -6.0                                  16. 0.01% alginate          -5.0   -5.5 -5.5                                  17. 0.1% polymannan         -5.5   -5.5 -6.5                                  18. 0.1% galactose          -4.5   -5.0 -5.0                                  19. 0.1% lactose            -5.0   -5.0 -5.0                                  20. 0.1% glucose            -5.0   -5.0 -5.0                                  21. 0.01% arabinose         -5.0   -5.0 -5.0                                  22. 0.01% sucrose           -5.0   -5.0 -5.5                                  ______________________________________                                    

As can be seen in Table 2 above, the extracts produced with the aid of asolution of pectin, polysaccharide or sugar have a mean nucleatingtemperature of the order of -5.5° C. For comparison, a pure solution ofpectin, filtered or otherwise using a membrane of porosity 0.45 μm(Sartorius), has a nucleating temperature of less than -10° C.

Furthermore, a berry extract produced with the aid of a solution ofpectin which is filtered using a membrane of porosity of 0.45 μm retainsa nucleating activity of -5.5° C. This therefore suggests that theactivity is not linked to the presence of a microorganism present in orat the surface of the berry.

Finally, when the extraction of a pellet of ground and centrifugedberries is repeated several times in succession using each time 12.5volumes of an aqueous solution comprising 0.1% pectin, for 15 minfollowed by a centrifugation, a good nucleating activity is stillobserved in the 25th extract. Table 3 below presents the nucleatingactivity of the successive extracts obtained in this manner, whichactivity is determined according to the glass tube test.

                  TABLE 3                                                         ______________________________________                                        Nth berry tissue extract                                                                     T20        T50    T80                                          ______________________________________                                         5             -5.0       -5.5   -5.5                                         10             -5.0       -5.5   -5.5                                         15             -5.0       -5.5   -6.0                                         20             -5.5       -6.5   -7.0                                         25             -5.5       -6.0   -6.5                                         30             -5.5       -7.0   -7.5                                         ______________________________________                                    

Nucleating activity dependent on the maturity of the berry:

The seasonal nucleating activity of a juice from sea buckthorn(Hippophae rhamnoides) berries harvested in the locality of Trondheim(Norway) is measured.

At the beginning, towards mid-July, the berries are small and green,containing very little juice. Accordingly, the July and August samplesare prepared by mixing the berries with a volume of deonized water andthen by crushing them with the aid of a mortar, whereas the samples forthe months of September to October of orange colour are prepared bycrushing the berries with the aid of a mortar (without adding water).The samples employed are obtained after centrifugation of the preparedsamples (5,000 g_(n), 10 min) and filtration of the supernatant througha filter of porosity 0.45 μm. The nucleating point of the extracts isfinally determined according to the abovementioned method.

The drawing figure illustrates the variation of the nucleating point asa function of the date on which the abovementioned berries wereharvested.

It is observed that the best nucleating activity relates to the berriesfrom the months of September and October, therefore to the ripe berries,of orange colour.

The degree of maturity of the berries can also be assessed moreprecisely by measuring their water content, using means known to aperson skilled in the art. This measurement was carried out for theabove-mentioned berries from July to October: the best nucleatingactivity was found in the berries of the month of September, whichpresent a water content of between 80% and 90%.

Nucleating activity of sea buckthorn leaves

Sea buckthorn (Hyppophae rhamnoides) leaves are ground and thenucleating agent is extracted therefrom using a solution of pectin orsugar in the same manner as described for the preparation of the berryextracts having the numbers 5 to 22 above.

In all cases, the mean nucleating activity of the leaf extractsdetermined by the glass tube test is of the order of -5.5° C. The seabuckthorn leaves are therefore also not a negligible source ofnucleating agents.

Purification, characterization

The nucleating agent from sea buckthorn can be purified by the methodbelow, for example. The agent can then be characterized by variousmethods.

Sea buckthorn (Hyppophae rhamnoides) berries are pressed bycentrifugation and 1/3 of the volume of distilled water is added to thejuice. The mixture is then centrifuged (5,000 g_(n), 10 min), then thesupernatant is filtered on a membrane of porosity 0.45 μm (Minisart,Sartorius). The filtrate is then loaded onto a gel filtration column2.6×60 cm containing a Sephacryl HR 300 resin, and eluted at 4° C. witha 0.05M Tris buffer of pH 7.5 (240 ml/h). The first elution peak hasnucleating activity (it is known that for this type of column, thevolume of eluate corresponding to the first elution peak containsmolecules of very high molecular weight).

The nucleating agent therefore comes from the sea buckthorn and not froma bacterium present in the berry (filtration on a membrane of porosity0.45 μm). Furthermore, this agent is a molecule of high molecularweight.

The eluate containing the nucleating agent is then analysed bypolyacrylamide gel electrophoresis. The SDS-PAGE electrophoresis (in thepresence of SDS') reveals the presence of a protein with an apparentmolecular weight of 25 to 27 kD (kilodalton).

Finally, PAGE electrophoresis (without SDS) on a large-porosity gelproves to be impossible, in spite of the pre-treatment of the eluatewith chloroform in order to remove lipid from the protein and in spiteof the use, in the gel, of non-ionic detergent (0.5% Triton X-100) or of7M urea.

Consequently, the nucleating agent is probably an aggregate of highmolecular weight which comprises a protein part which can be attached tocellular structures which are too small to be retained on a 0.45 μmfilter, but too large to migrate in a non-denaturing polyacrylamide gel.Furthermore, these cellular structures could also participate in thenucleating activity. Finally, the protein part is a protein whichcomprises subunits with an apparent molecular weight of 25 to 27 kD.

Inactivation

The nucleating agent is subjected to chemical treatments in order todetermine the structures which are essential for the nucleatingactivity.

A lipid-removing treatment is performed on the purified nucleatingagent. For that, 2.5 volumes of chloroform are mixed with 1 volume ofpurified agent, the mixture is stirred, it is allowed to stand for 24hours at 4° C., then the chloroform is extracted by the action of airbubbles. A fraction containing lipid-free agent and a fractioncontaining lipids are thus obtained. When the nucleating activities ofthe purified agent and 4° C. the lipid-free agent are compared, adecrease of 4° C. in the nucleating point is observed following thelipid-removing treatment. Lipids therefore seem to play a role in thenucleating activity.

Furthermore, if the lipid fraction is mixed with the fraction containingthe lipid-free agent for 14 days at 4° C., and then the nucleatingactivities of the mixture and of the fraction containing the lipid-freeagent compared, an increase in the nucleating point of 3° C. isobserved. Consequently, lipids contribute to the production of a highnucleating activity.

The nucleating agent may therefore also comprise a lipid part.

The effect of mercaptoethanol and of 0.01M SDS is measured at various pHvalues, on crude berry extracts. Mercaptoethanol has no effect on thenucleating point, which indicates that disulphide bridges are notessential for the nucleation. And the effect of SDS on the nucleatingpoint is relatively limited (0° to 1° C. according to the pH), whichindicates that the positive charges at the surface of the agent are notessential for the nucleating activity (SDS adds an excess of negativecharge to the protein and thereby masks the positive charges present atthe surface of the protein). Likewise, the pH appears not to influencethe behaviour of the nucleating agent.

Finally, the action of N-bromosuccinimide (NBS) on the nucleating pointof the agent is analyzed. The mixture of purified nucleating agent andNBS (final concentration 0.001M) is adjusted to pH 3.0 by adding smallquantities of 2M HCl, and it is then left for 30 minutes at 25° C.before being readjusted to pH 7.5 by adding small quantities of a Trisbuffer. The determination of the nucleating point before and aftertreatment reveals a decrease of 2.8° C. in this point. This indicatesthat aromatic amino acids are important for the nucleating activity (NBSoxidizes the indole groups and the tyrosines).

The following examples are presented by way of illustration of thevarious industrial applications of the nucleating agent according to thepresent invention, in a process for freezing freezable products, in aprocess for freeze-texturing a freezable food product, and in a processfor concentrating a food liquid.

EXAMPLE 1

A raw juice from ripe sea buckthorn berries is prepared by grinding theberries and then by recovering the supernatant therefrom aftercentrifugation.

It is then added to an ice cream, during its preparation in atraditional manner, in an amount of 1 volume per 600 volumes of icecream. Then the cream is frozen at -8° C.

For comparison, an ice cream prepared in a traditional manner, withoutaddition of a sea buckthorn berry juice, is frozen at -12° C.

EXAMPLE 2

A sea buckthorn berry extract is prepared by first grinding berries,then by adding thereto 10 volumes of a 0.1% solution of pectin which isallowed to react for 15 min, then by centrifuging the mixture at 10,000g for 10 min so as to recover the supernatant therefrom.

The sea buckthorn berry extract thus prepared is then added to a meatmousse, during its preparation in a traditional manner, in an amount of1 volume per 100 volumes of meat mousse. Then the meat mousse is frozenat -10° C.

For comparison, a meat mousse prepared in a traditional manner, withoutaddition of a sea buckthorn berry extract, is frozen at -15° C.

EXAMPLE 3

A soya bean protein paste is prepared by heating at 70° C. for 10minutes a soya bean protein isolate containing 20% protein, then bycooling the solution to 20° C. The sea buckthorn berry juice describedin Example 1 is added to this paste in an amount of 1 volume per 100volumes of this paste. The paste which is present in the form of a thinlayer 2 to 5 mm thick is frozen at an average rate of the order of 0.1°C./min down to -20° C., then this temperature is maintained for 10hours. Finally, in order to stabilize the paste texture modification, itis freeze-dried and then heated at 100° C. for 2 minutes. The soya beanpaste then has a fibrous and lamellar texture. This texture is verysimilar to the texture of "cornflakes".

For comparison, the same paste composition is frozen without raw berryjuice, freeze-dried and then heated under the same conditions as above.A paste having a spongy and disorganized texture which is not at allsimilar to the texture of "cornflakes" is thus obtained.

EXAMPLE 4

0.03% of the sea buckthorn berry juice described in Example 1 is addedto a coffee extract comprising 10% dry matter. The mixture is cooled at-6.5° C. for 30 min, then centrifuged at 2,000 g for 15 min at -5° C.,and the supernatant is harvested. The liquid phase is thereby separatedfrom the crystalline phase of the mixture and a coffee extractcomprising 15.3% dry matter is thus obtained.

For comparison, the same coffee extract comprising 10% dry matter doesnot freeze in the absence of the nucleating agent according to thepresent invention.

We claim:
 1. A process for increasing the temperature at which a foodproduct freezes comprising adding to a food product a substance selectedfrom the group consisting of juice obtained from berries of seabuckthorn and an aqueous extract obtained from sea buckthorn tissueselected from the group consisting of berry tissue and leaf tissue.
 2. Aprocess for preparing a food product which during preparation issubjected to a temperature for freezing the food product comprisingadding to a food product a substance selected from the group consistingof juice obtained from berries of sea buckthorn and an aqueous extractobtained from sea buckthorn tissue selected from the group consisting ofberry tissue and leaf tissue and then cooling the food productcontaining the added substance to a temperature for freezing the foodproduct containing the added substance.
 3. A process according to claim1 or 2 wherein the substance is an extract obtained from sea buckthornberry tissue.
 4. A process according to claim 3 wherein the berry tissueis tissue obtained from sea buckthorn berries having a water content offrom 80% to 90%.
 5. A process according to claim 1 or 2 wherein thesubstance is obtained from sea buckthorn berries having a water contentof from 80% to 90%.
 6. A process according to claim 2 wherein the foodproduct containing the added substance is cooled to a temperaturebetween -5° C. and -25° C.
 7. A process according to claim 6 wherein thesubstance is an extract obtained from sea buckthorn berry tissue.
 8. Aprocess according to claim 2 wherein the food product containing theadded substance is cooled to a temperature between -5° C. to -10° C. 9.A process according to claim 2 wherein the food product containing theadded substance is cooled to a temperature for obtaining a frozenproduct for freeze-drying and further comprising freeze-drying thefrozen product to obtain a dried food product.
 10. A process accordingto claim 9 wherein the substance is an extract obtained from seabuckthorn berry tissue.
 11. A process according to claim 9 or 10 whereinthe food product is a soy bean protein isolate.
 12. A process accordingto claim 2 wherein the food product containing the added substance iscooled to a temperature for freezing so that a crystalline phasecontained in a liquid phase is obtained and further comprisingseparating the liquid phase from the crystalline phase to obtain aconcentrated liquid phase food product.
 13. A process according to claim12 wherein the substance is an extract obtained from sea buckthorn berrytissue.
 14. A process according to claim 12 or 13 wherein the foodproduct is a liquid coffee extract.
 15. A process according to claim 12or 13 wherein the food product is selected from the group consisting offruit juice and vegetable juice.
 16. A process according to claim 2wherein the food product is an ice cream composition and the substanceis added during preparation of the ice cream composition and thenfreezing the composition and added substance.